Dissociation of supplementary motor area and primary motor cortex in humansubjects when comparing index and little finger movements with functional magnetic resonance imaging

This study provides the first investigation of supplementary motor area (SM A) and primary motor cortex (MI) activation with similar movements differin g only in subjective difficulty of motor control. Brain activation with sim ple tapping of the right index finger (well trained during daily life and e asy to perform) was compared with tapping of the little finger (less traine d and difficult to perform) using functional magnetic resonance imaging at 3 Tesla. Due to optimised movement standardisation, extrinsic influences on activation levels such as movement complexity, amplitude and frequency wer e minimised. Fifth finger tapping significantly increased the number of act ivated SMA voxels by 450% whereas MI activation showed no significant diffe rence between fingers. We conclude that with similar movements the degree o f subjective difficulty specifically modifies SMA but not MI activation. (C ) 2001 Elsevier Science Ireland Ltd. All rights reserved.